Recently, light, thin, short, small and flexible displays have been actively researched.
A glass substrate used for conventional displays has a thickness of about 0.4˜0.5 no matter how thin one tries to fabricate it, but on the other hand, a polymer substrate for flexible displays has a thickness of about 0.1˜0.2 Further, the weight of the polymer substrate is ⅕ or less than that of the glass substrate, so that the polymer substrate has a much lighter weight than the glass substrate.
Moreover, the polymer substrate has a much higher durability than that of the glass substrate. Meanwhile, from the point of view of manufacturing process, displays employing a glass substrate are sequentially manufactured one by one through a batch process, but on the other hand, flexible displays employing a polymer substrate can be manufactured in large quantities through a roll-to-roll process.
The structure of such a flexible display is roughly described as follows.
Referring to FIG. 1, a flexible display includes a polymer substrate 10 and a device part 20 formed on the polymer substrate 10. The device part 20 may be embodied as display unit devices, and, from the point of view of function, includes an image display layer 22 for display an image and a driving pixel unit layer 24 for driving the image display layer 22.
When external warping stress, which is a force necessary for deforming a display in a predetermined curvature, is applied to this flexible display, the polymer substrate and the device part are elastically deformed. If the external warping stress is applied thereto within the elastic limit of the polymer substrate, the polymer substrate returns to its original state the moment the applied external warping stress is removed. However, if the external warping stress exceeds the elastic limit of the polymer substrate, the polymer substrate does not return to its original state, and is rendered plastically deformed.
As is well known to those skilled in the art, the elastic limit of the polymer substrate influences the aforementioned flexibility. In particular, a flexible display, for example, an electronic paper which is rolled as a roll of paper, must have a high flexibility.